1. Field of the Invention
The present invention relates to a runner liner of fluid machine such as water turbine, pump turbine, pump and the like. More particularly, the invention is concerned with a construction of the runner liner which is attached to the periphery of the runner of a fluid machine so as to constitute a seal in combination with a stationary part of a runner chamber accommodating the runner.
2. Description of the Prior Art
Fluid machines are machines for extracting energy from fluids or, alternatively, delivering energy to the fluid. Water turbines and pumps are typical examples of the former and latter type fluid machines. In addition, there is a fluid machine called pump turbine, which can perform both of above-mentioned two functions. Although the present invention is applicable to all kinds of fluid machines as mentioned above, an explanation will be made hereinafter specifically in connection with a water turbine or pump turbine, by way of example, in order to clarify and simplify the explanation of the invention.
In general, a water tubine has a runner, a runner chamber accommodating the runner and a main shaft attached to the runner. In operation, water of a large head is introduced into the runner chamber and acts on the runner to rotate the same. The rotation of the runner is transmitted, through the main shaft, to a generator adapted to produce electric energy. After delivering the energy to the runner, the water is discharged out of the runner chamber.
In case of a pump turbine, a pumping operation can be performed in the reverse manner. Namely, the runner is driven by externally supplied electric energy, so as to suck water of low pressure into the runner chamber, and to pressurize the water. The pressurized water is discharged out of the runner chamber at a high pressure. Thus during the pumping operation of the pump turbine, the direction of flow of water is reverse to that in ordinary water turbine.
Since the runner is rotated while the wall of the runner chamber is fixed, a suitable gap has to be preserved therebetween. In operation, the water of high pressure is liable to leak through this gap, resulting in a reduction of efficiency of the water turbine and pump turbine.
To avoid this, the gap between the periphery of the runner and the wall of the runner chamber is set extremely narrow, so as to prevent the water of large head to leak therethrough.
The peripheral portion of the water turbine or pump turbine is, however, inconveniently eroded by the water of high pressure and ground upon contact with the opposing wall surface of the runner chamber, as it works for a long period of time.
Consequently, the gap between the peripheral portion of the runner and the wall of the runner chamber grows large to increase the rate of leakage of the high pressure water.
It is therefore necessary to regenerate the eroded and ground peripheral surface of the runner. The work for the regeneration is, however, extremely expensive and time consuming, for the following reasons.
Firstly, in order to extract the runner from the runner chamber, it is necessary to demount parts such as head cover, main shaft, main shaft bearing, and the generator.
Secondly, the regeneration itself is a troublesome work which consists in cutting and removing the defective parts in the peripheral surface of the runner, making a build-up welding and then finishing the built-up surface at a required precision.
In order to simplify and facilitate the regeneration work, it has been proposed to use a liner (referred to as runner liner in this specification) attached to the periphery of the runner. According to this proposed method, the eroded and ground peripheral surface can be regenerated simply by renewing the liner. The liner conventionally used is, however, an integral ring-shaped liner adapted to be fit around the runner. It is therefore necessary, in order to renew the liner, to extract the runner from the runner chamber. Thus, this solution is still unsatisfactory, because of the previously mentioned first reason.